Texture of Metamorphic Rocks

Metamorphic texture refers to the size, shape, and arrangement of mineral grains. It is determined by the environment of formation (temperature and pressure).

1. Foliated Textures

Results from Differential Stress. Minerals align in parallel layers or bands.

[Important Button] View Foliation Grades
  • Slaty: Microscopic flakes (e.g., Slate).
  • Phyllitic: Silky, wavy sheen (e.g., Phyllite).
  • Schistose: Large, visible mica scales (e.g., Schist).
  • Gneissic: Alternating dark/light mineral bands (e.g., Gneiss).

2. Non-Foliated Textures

Forms under Confining Pressure where grains are equidimensional (equal in all directions).

[Important Button] Key Examples

Granoblastic: Mosaic-like grains (e.g., Marble, Quartzite).
Hornfelsic: Randomly oriented grains from contact metamorphism.

3. Special Textures

Sometimes, specific crystals grow much larger than the surrounding matrix.

[Important Button] Porphyroblastic Growth

Porphyroblasts: Large crystals like Garnet or Staurolite surrounded by a fine-grained groundmass.

Chemical stability formula: ΔG = ΔH - TΔS